Various metals are useful in many industrial processes. However, due to undesirable chemical reactions, e.g., environmental oxidation, a passive layer can form on the surface of the metals. Such passive layers can decrease the amount of useful surface area of the metal.
For example, metallic replacement technology is one method that is often utilized to remove metal ions from aqueous waste solutions (hereafter also referred to as aqueous process solutions). In this technology, iron is contacted with aqueous process solutions containing metal ions. As is well known in the art, the metal ions in the aqueous process solution are removed by reaction with the iron surface. As a result of chemical reactions that can occur in an oxygen rich environment, however, a passive layer of iron oxide can form on the surface of the iron metal. It is believed that the metallic replacement does not occur with the passive layer. Since the passive layer can significantly reduce the surface area of iron metal available to provide metallic replacement, the amount of metallic replacement can be reduced proportionally to the available surface area.
Similarly, passive layers can form on the surface of many metal catalysts, which results in a decrease of useful surface area. Since the rate of the total reaction is typically proportional to the available surface area of the metal catalyst, total reaction rates can be improved by removing these passive layers.
Accordingly, there is a need for reducing the passive layer that can form on the surface of various metals.